Turbos For The Street

In essence, a turbocharger is a simple device. Basically, a high-tech pinwheel that pushes air into an engine, it's powered by the combination of exhaust heat and pressure, harnessing power that would otherwise be lost out of the tailpipe. This makes turbocharging an ideal way to increase the power of an engine far beyond what natural aspiration will allow. Turbochargers make power more efficiently than superchargers do, because the engine isn't using power from the crankshaft to drive it. And over time, a turbo kit will likely cost less than nitrous (taking into account the cost of refilling the bottle), so turbochargers may be the best power-adder around.

As simple as turbochargers are, much mystery still surrounds them. Flip through a turbocharger manufacturer's catalog, and you will find dozens of different models in a dizzying array of sizes. On top of that are dozens of graphs and cringe-inducing mathematical formulae that may make you want to poke your eyes out. Which one is best for my car? Where do I install them? How much power can I make? Like so many of life's nagging questions, the answer to all of these is, "it depends."

The short answer is you can make as much power as you can afford to spend. Want 2,000 hp? A turbocharger will certainly get you there, though you need an engine and drivetrain that will support it, though its operating range will be quite narrow. Here's a simple rule of thumb: Turbochargers can basically double the power output of a well-made stock engine. And that's just the starting point. 1,000hp builds aren't outrageous, especially on a modern V8, and the engine combination needed to make that much power is remarkably mild. With a pair of turbochargers, it is not difficult to build a 1,000hp daily driver.

In this article, we touch upon some of the major points to consider when planning a turbo build of your own, offer advice from the pros, and document some effective, homebuilt combinations. First, though, let's define some terms.

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Inducer, Exducer, and Trim
Notice how the blades of the compressor and turbine wheels are narrow at the top and wider at the base? The calculation of the difference in diameter between the top and bottom of the wheel is the trim. Generally, a larger trim number means that particular wheel will move more air than one with a smaller number.

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The terms inducer and exducer refer to the parts of the turbine and compressor wheels that face the inlet and outlet sides of their respective housings. On the compressor wheel, the small diameter is the inducer because it draws air in from the center opening. On the turbine wheel, the bottom is the inducer because exhaust gas enters from the side and exits through the center opening.

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A/R Ratio
Area Radius ratio (A/R) refers to how much the volume of the housing decreases from the air inlet to the compressor or turbine wheel. In colloquial terms, think of this number as a calculation of how much smaller the volute (the "snail shell") becomes as it twists to the center of the housing. The area-ratio figure has the most profound effect on the exhaust side. A smaller A/R increases the velocity of exhaust gas to the turbine wheel faster than a larger A/R housing will. This affects how rapidly the turbocharger will spool up and start to make boost in the intake.

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Lund Racing: Pro Turbo Builders
Armed with some terminology, we started talking with some pro builders who are making incredible power with turbochargers as their ally.

Ken Bjonnes Lund Racing
For several months, we've followed the progress Ken Bjonnes has been making with Lund Racing's twin-turbo '11 Mustang, but we finally got to see it in person early this year at the NMRA's Spring Break Shootout at Bradenton Motorsports Park. Full details of this car can be found on page 10 of this issue, so we won't rehash them here. We did take the opportunity to talk with Ken at length about turbocharging, though.

"The biggest problem people have is they don't plan ahead," Ken says. "How much power do you want? How much room do you have? And how much money do you want to spend? Those are the first questions a person needs to address when planning a turbo build," he continued. "People tend to pay attention just to the turbo, but the turbo is one part of a complicated system."

When asked about the decision to install a single turbocharger or go with twin turbos, Ken says he prefers twin turbos on a V8 for street cars. Race cars that operate in a limited rpm range may benefit from a large, single turbocharger, but for a street engine, which needs to make power below the torque and horsepower peaks, a twin-turbo system will generally be more responsive and enjoyable to drive in traffic. In addition, Ken stressed the importance of getting air to the turbocharger efficiently, both on the inlet and exhaust sides. "The inlet size is important. The turbos need a large area of clean air [to draw from], and there shouldn't be a pressure drop anywhere in the inlet system." On the exhaust side, Ken likes to see as simple of a header as possible directing exhaust into the turbine. "Look at it this way, would anyone put five 90-degree bends on their cold-air intake?"

Lastly, Lund Racing and all the pros we talked with emphasized quality wastegates and bypass valves as critical to controlling boost. Cheap parts can be inconstant, and you can end up overspeeding the turbocharger or creating a situation where boost pressure rises above the bypass valve's rated limit. Boost creep, as this is known, can kill your engine in a hurry, especially if you're pushing the limits of your parts already. Where you place the wastegates also affects how efficiently and accurately they operate. Ken likes to place them close to the turbochargers, and if there's a bend at the pipe going into the turbocharger, the top of that bend is the ideal placement. This is where exhaust pressure will be the highest between the engine and turbocharger, so placing the wastegate there allows the most accurate control of boost.

Eddie Rios
Addiction Motorsports

We chose Eddie Rios's shop, Addiction Motorsports, as the location to shoot this month's cover. Rios has nearly a decade of experience building and tuning both carbureted and fuel-injected race cars. He built a turbocharged Mustang that made 866 hp at the wheels and was featured in the Dec. '06 issue of Modified Mustangs & Fords, so he knows turbochargers, too. He told us the biggest mistake his customers make is buying a turbocharger just because it was cheap, then asking him to make it work on their cars. "People come up to me and say, ‘I have this turbo…' and I have to break their hearts," he says. "The turbocharger needs to be sized right. If it's too big, it won't spool. If it's too small, [boost] will come on too fast, and there will be no top-end power." He knows from experience what turbochargers to recommend to his customers, but he suggests people research some of the online sizing guides and consult owners of cars with similar combinations. Rios echoed Ken Bjonnes warnings against inexpensive wastegates: "Some have two-piece seats that aren't installed correctly. They leak pressure and won't build boost."

Josh Deeds
Deeds Performance

Eddie Rios directed us to Josh Deeds' shop. He does custom fabrication work for street and race cars and has years of experience with turbochargers. A guy who doesn't mince words, Josh began our discussion by saying, "Almost everyone makes this mistake: They buy junkyard turbos like a Garrett P38 off a 7.3L diesel, which was designed to work within an operating range of 3,000 [engine] rpm, and they want to put two of them of their car. Will it work? Yes, but it won't come in until 5,000 rpm, and below that the engine won't make power. If the turbo is sized right, there should be as little lag as possible." So how do you know which size is right? Josh says the online sizing guides can be useful to getting you close to the right size for your application, but you're better off asking someone with experience building and racing turbo cars. Walk around the pits at the track and see who're using what and how well it's working. You'll likely find a person willing to share advice and information.

Another common problem Josh has seen is with the oil return from the turbocharger. The bearings are fed pressurized oil from the engine, which lubricates the bearings, then drains back to the oil pan through a low-pressure return hose. Some people encounter problems when the turbos are located below the oil level in the pan. Without gravity to drain the oil, it will pool up in the bearing housing and eventually leak past the seals, and you'll begin to see blue smoke in the exhaust. Some people will try to remedy this by installing a fluid pump to send oil back to the oil pan, but that doesn't always solve the problem. According to Josh, "Oil gets whipped up as it passes through the bearings because the shaft speed of turbochargers is very high. It turns to foam, and pumps don't do very well pumping air, so it may not be able to scavenge the oil well enough to prevent it from leaking past the seals. You still may have smoke in the exhaust, even with a pump." If you can't locate the turbos above the oil pan, Josh recommends adding a catch can between the oil outlet and the pump. The catch can will separate the air from the oil, which can then be more efficiently pumped back to the pan.

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Tom Nelson
Nelson Racing Engines

Any muscle-car enthusiast with access to YouTube knows of Tom Nelson and Nelson Racing Engines, famous for building twin-turbo, V8-powered cars. "My dad built a twin-turbo Pantera at home when I was about 11 or 12. Back then, that car was a lightning ship," he tells us. It also hooked him on turbochargers as his power-adder of choice. It has served him well, too, gaining Internet fame through dyno-room videos and in-car shenanigans in and around his modest Chatsworth, California, shop.

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Tom recently introduced his own line of turbochargers—he calls them Mirror Image or Symmetrical turbochargers. The castings are available with left or right turbine inlets and compressor outlets. That way, you can build an underhood twin-turbo system for a V8 car with intake plumbing that is the same on the left- and righthand side of the car. Tom admits he did this mostly for aesthetics and ease of packaging, but there may also be a slight power advantage, as well. Either way, builders now have more options when laying out a custom turbo system. Tom's turbochargers come with billet compressor wheels and Inconel turbine wheels, and the design of the fins is more aggressive, which means they spool up faster. The pricing is in line with current high-quality turbo manufacturers' models.

Tom was less enthusiastic about using compressor maps as sizing guidelines for your particular application. "What I've fought for years is the notion that people think they need a smaller turbo. That's a total misconception. If the turbo is too small, all it does is become a heat pump," he says. We all know that hot air does not make horsepower, either. Tom says compressor maps can be deceiving, and that similarly sized turbochargers from the same manufacturer can operate quite differently when they are actually installed on a car. "The A/R ratio doesn't always correspond with performance. The best way to pick a turbo is to ask experienced people. Take advice from someone who's done it already."

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Once you have turbos picked out, Tom recommends building the engine with the best parts you can afford. He likes 2618 aluminum-alloy pistons, "They are a little loose on start-up, but they take abuse; 4032 [alloy] is not as tough. Keep boost to between 6 and 7 psi with those pistons." For piston rings, Tom prefers 1⁄16-inch non-coated rings, and he sets the top ring gap at about 0.024 inch. He gaps the second ring a little wider than that, and he recommends using pistons with a V-groove between where the first and second ring lands. His reasoning is that with high cylinder pressure, you're going to have more blow-by than a naturally aspirated engine. The V-groove and wider second ring gap give blow-by gases a place to go. Otherwise, the pressure can build up behind the top ring and affect the way it seals to the cylinder walls. Tom also recommends using cams with 260 degrees of advertised duration or less for street engines. "Too much overlap takes the fresh charge and sends it out the exhaust," he says. For his custom cam grinds he uses large-base circle cams with special exhaust lobes that open the exhaust valve gently, allowing cylinder pressure to bleed down. Otherwise, a fast-opening exhaust valve will be hard on the cam and valvetrain because it has to fight the extra cylinder pressure of a boosted engine.

Gale Banks
Banks Power

As impressive as their resumes are, none of the pros we've interviewed so far can claim to have put more turbochargers on engines than Gale Banks. He's been experimenting with turbochargers since 1966, when he started building twin-turbocharged, big-block Chevys for race boats. He described a twin-turbo, fuel-injected, 1,800hp 430 big-block running on alcohol that he built in 1976. He blames this engine for getting turbochargers banned from Off-Shore boat racing for decades. Success in boat racing led customers to his shop asking for turbochargers for their cars, and Gale branched out to all forms of motorsports as well as high-performance street engines.

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Gale believes turbos are finally here to stay. “I was lobbying the OEs in the ’80s during the second oil crisis,” he says. Now, Ford and Chevrolet are rolling out turbocharged 4- and 6-cylinder engines across their model lines, not just on a few limited-production models. For the aftermarket, Gale tells us he’s working on a compound (turbocharged and supercharged) LSX engine package. The twin-turbo small-block in this picture is a package Gale has offered for a few years. The turbos force-feed a port fuel injected manifold. Though an intercooler is available, the base package doesn’t include one. Instead, Gale, recommends a water/methanol injection kit to cool the intake charge. Power levels range from 800–1,100 hp and this engine can be daily driven. Another cool feature is the cast-iron exhaust manifold design. The narrow design places the turbochargers close to the engine in a neat, compact package that should fit in nearly any Chevrolet from the muscle-car era.

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Home Builders
Weekend warriors need not be intimidated by turbocharging. Here are a few regular guys who've built effective combinations at home.

Joshua Minder
1972 Plymouth Duster
We think all our readers can appreciate Josh Minder's '72 Plymouth Duster with a homebuilt, turbocharged 225 CID Slant Six. Josh bought this car from his next-door neighbor when he was 17, and in just four years, he's transformed it into this cool sleeper you see here. He didn't have much money to spend, so a V8 swap never really entered his mind, but when a friend gave Josh a used Toyota Supra turbocharger, Josh and his father, David, got to work scrounging junkyards and online parts listings. In addition to crafting the turbo system, David and Josh also straightened and painted the car themselves, and Josh tells us he had the car finished just 30 minutes before he had to leave for his senior prom. On the road, he surprises lots of unsuspecting sports cars, routinely walking away from the swarms of Porsches and Mercedes that litter the roads and freeways of Southern California. Imagine how those Europhiles must feel, getting spanked by a throw-away car that sounds like a UPS truck.

11/15The father and son pair had to install a Walbro fuel pump, because the mechanical pump didn’t maintain enough pressure. Under boost, fuel was pushed backward in the fuel lines. They then converted a naturally aspirated Holley fuel-pressure regulator to reference boost and added a return line to the gas tank. Other than the Offenhauser intake manifold, the engine is a completely stock 7.8:1 compression Slant Six. David says the stock cam works perfect for turbocharging because it’s so small, and Josh says the car now makes huge torque. It’s taken apart in these pictures because Josh broke some teeth off the timing gear while doing CC-approved burnouts in front of some hot chicks in Huntington Beach, California. We will do an in-depth car feature on Josh’s Duster when it’s back together.

Randy Seward
1991 Ford Mustang

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Watching Randy Seward's Mustang click off 8-second passes at Bradenton Motorsports Park during the NMRA Spring Break Shootout, we wondered if it was time for an eye exam. How could this plane-jane Notchback be so fast? Aside from the Garrett stickers on the sides, there is no indication that this is anything other than the secretary's car Ford intended the non-GT Mustangs to be. Randy was the overall winner in True Street that weekend, and this was not the first time that's happened. In all, he's taken home four King of the Street trophies, with more likely to come.

Randy is an engineer, so it wasn't a surprise to learn he designed the turbo system in his Mustang. He said the turbocharger-sizing guide on Garrett's website is very good, because it walks you through how to calculate the volume of air your engine needs to move to make the amount of horsepower you desire. Determining those parameters will narrow the choice of turbochargers to a relatively easy choice.

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Based on his personal experience, Randy tells us turbochargers don't like backpressure in the system after the turbine, so he designed his system such that the exhaust gas enters the turbine housing from above, then exits the turbocharger straight back toward the firewall. Randy purposely kept the tubes leading away from the turbochargers as straight as possible before dropping down under the car into a 3-inch Flowmaster exhaust system.

His combination consists of a Dart block, forged internals, and Trick Flow cylinder heads. He stressed the importance of quality cylinder heads with a good sealing surface. That, combined with quality head gaskets, keep combustion pressure contained within the cylinders where it's supposed to be. He likes a 9.0:1 compression ratio, claiming it provides a good compromise of off-boost power for street driving without being too much at the track. Judging by the fact that Randy's car is making somewhere in the neighborhood of 1,100–1,400 hp and has run a best time of 8.45 at 164 mph, we think he's on to something. Need more convincing? Randy drives his car about 5,000 miles per year to and from the events he competes in.

Some of our friends from the Brotherhood of Street Racers shuffled some parts around and concocted this hooptie: a turbocharged TPI engine running on E85 in a 1980 Oldsmobile Cutlass. The best guess anyone of them can come up with is that the car cost them a total of $2,000 to build. It's not much to look at, but that's seen as an advantage to these guys. We snapped these pictures at Vehicle Liquidation Used Cars in Littlerock, California, where the sales guys were more than willing to go along with the joke, offering to give this pile to anyone with guts enough to take it home.

The engine is out of a Suburban from the junkyard, as are the TPI intake parts. It runs on MegaSquirt's V3 ECM, which is capable of handling up to 21 psi of boost. The turbocharger is one of those really cheap, no-name ones from eBay, and it breathes directly into the engine rather than running through an intercooler. Intake temperatures are not a concern, because the car is fueled by E85, which has a lower latent heat of vaporization than gasoline. You can feel this yourself by dripping some alcohol on your skin. As it evaporates, the alcohol pulls a lot of heat from the area, making your skin feel cold. In an engine, E85 and other alcohol-based fuels can lower temperatures in the intake by 50 degrees or more. The rest of the drivetrain is stock, and probably the only reason the transmission and rearend aren't smoldering piles of parts (yet) is because the turbocharger is big. Very little thought was put into choosing it; a 77mm unit was picked basically because someone thought it sounded good. It doesn't spool quickly, so power comes on gradually, making it easier on the stock parts. "You can make junk parts run," say our racer buddies, implying that all you need is a bigger turbo. There are limits to this, however, and it's likely that, in the case of this combination, the engine is done revving before the turbocharger is close to making enough boost to wipe out the bottom end of this block. The point is that even a mismatched combination can be fast.

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Wrap-up
We've ventured into the world of turbocharging before, most notably with Ted Toki's 1955 Chevy in the Sept. '10 and Apr. '11 issues of Car Craft, but we felt it was time to revisit the issue now. We will be building on this foundation with more in-depth coverage of turbo builds, and we'll even tackle a few of our own, including the concoction Editor Glad is brewing for his 71 Demon. In the meantime, check out some of these online resources for more information, and email us with ideas of your own at CarCraft@CarCraft.com.